The adipose conversion of 3T3 cells, an established mouse fibroblast line, is one of the simplest forms of differentiation that takes place under cell culture conditions. The process is rather easily controlled, and indications to date strongly support the idea that this process is a faithful model of adipocyte formation in the tissues of developing animals and humans; but it is vastly easier to study the adipose conversion in culture than to study adipose tissue formation in animals. The accumulation of lipid is due to increased rates of triglyceride synthesis, brought about by broad activation of the participating enzymes and the development of hormone sensitivity. It is proposed to study this phenomenon broadly, including both basic and applied aspects.